fix compile xdp-forward fail

[calcky]

OS: ubuntu2204.localdomain 5.15.0-91-generic
compile error:
xdp-forward.c: In function ‘do_load’:
xdp-forward.c:139:24: error: implicit declaration of function ‘bpf_object__next_program’; did you mean ‘bpf_object__unpin_programs’? [-Werror=implicit-function-declaration]
139 | while ((prog = bpf_object__next_program(skel->obj, prog)) != NULL)
| ^~~~~~~~~~~~~~~~~~~~~~~~
| bpf_object__unpin_programs
xdp-forward.c:139:22: error: assignment to ‘struct bpf_program *’ from ‘int’ makes pointer from integer without a cast [-Werror=int-conversion]
139 | while ((prog = bpf_object__next_program(skel->obj, prog)) != NULL)
| ^
xdp-forward.c:140:21: error: implicit declaration of function ‘bpf_program__type’; did you mean ‘bpf_program__size’? [-Werror=implicit-function-declaration]
140 | if (bpf_program__type(prog) == BPF_PROG_TYPE_XDP &&
| ^~~~~~~~~~~~~~~~~
| bpf_program__size
xdp-forward.c:141:21: error: implicit declaration of function ‘bpf_program__expected_attach_type’; did you mean ‘bpf_program__set_expected_attach_type’? [-Werror=implicit-function-declaration]
141 | bpf_program__expected_attach_type(prog) == BPF_XDP)
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| bpf_program__set_expected_attach_type
cc1: all warnings being treated as errors
make[1]: *** [../lib/common.mk:107: xdp-forward] Error 1
make: *** [Makefile:40: xdp-forward] Error 2